The present invention relates to a method of operating an internal combustion engine in a motor vehicle in particular, where fuel is injected directly into a combustion chamber either during a compression phase in a first operating mode or during an intake phase in a second operating mode, with shifting between the two operating modes, and where the performance quantities that influence the actual torque of the internal combustion engine are controlled and/or regulated differently as a function of a setpoint torque in both operating modes. In addition, the present invention relates to an internal combustion engine for a motor vehicle in particular having an injection valve with which fuel can be injected directly into a combustion chamber either during a compression phase in a first operating mode or during an intake phase in a second operating mode, and having a control unit for shifting between the two operating modes and for differentiated control and/or regulation of the performance quantities that influence the actual torque of the internal combustion engine as a function of a setpoint torque in both operating modes.
Systems for direct injection of fuel into the combustion chamber of an internal combustion engine are known in general. A distinction is made between stratified charge operation as the first operating mode and homogeneous operation as the second operating mode. Stratified charge operation is used in particular at low loads applied to the internal combustion engine, while homogeneous operation is used at higher loads.
In stratified charge operation, fuel is injected into the combustion chamber during the compression phase of the internal combustion engine in such a way that there is a cloud of fuel in the immediate vicinity of a sparkplug at the time of ignition. This injection can be accomplished in various ways. Thus, it is possible for the injected cloud of fuel to be near the sparkplug and to be ignited by it during or immediately after injection. It is likewise possible for the injected cloud of fuel to be guided to the sparkplug by a charge movement and only then ignited. In both combustion methods, there is a stratified charge but there is not a uniform distribution of fuel.
The advantage of stratified charge operation is that the smaller loads applied can then be carried out by the internal combustion engine with a very small quantity of fuel. However, larger loads cannot be handled by stratified charge operation.
In homogeneous operation which is provided for such larger loads, the fuel is injected during the intake phase of the internal combustion engine, so that turbulence can be created in the fuel, which is thus distributed readily in the combustion chamber. To this extent, homogeneous operation corresponds approximately to the operation of internal combustion engines where fuel is injected into the intake manifold in the traditional manner. Homogeneous operation can also be used with lower loads as needed.
In stratified charge operation, the throttle valve in the intake manifold leading to the combustion chamber is opened wide, and combustion is controlled and/or regulated essentially only by the fuel mass to be injected. In homogeneous operation, the throttle valve is opened and closed as a function of the torque required, and the fuel mass to be injected is controlled and/or regulated as a function of the intake air mass.
In both operating modes, i.e., in stratified charge operation and in homogeneous operation, the fuel mass to be injected is additionally controlled and/or regulated at an optimal level with regard to saving fuel, reducing exhaust and the like as a function of several additional performance quantities. The control and/or regulation is different in the two operating modes.
The internal combustion engine must be shifted from stratified charge operation to homogeneous operation and back again. In stratified charge operation, the throttle valve is opened wide, and thus the air is supplied largely unthrottled, but in homogeneous operation the throttle valve is only opened partially and thus reduces the supply of air. Especially in shifting from stratified charge operation to homogeneous operation, the ability of the intake manifold leading to the combustion chamber to store air must be taken into account. If this is not taken into account, shifting can lead to an increase in the torque delivered by the internal combustion engine.
The object of the present invention is to provide a method of operating an internal combustion engine with which improved shifting between the operating modes is possible.
The object is achieved with the method and internal combustion engine according to the present invention by determining a change in the actual torque during a shifting operation and by influencing at least one of the performance quantities as a function thereof.
On the basis of the determination of changes in the actual torque during the shifting operation, it is possible to detect irregular running or jerking during shifting. After jerking has been detected, irregular running can be counteracted by influencing performance quantities. It is thus possible on the whole to prevent irregular running or jerking when shifting from homogeneous operation to stratified charge operation or vice versa. Shifting operations between the two operating modes are thus improved in particular with regard to increased running smoothness and thus greater comfort.
It is also possible for the change in the actual torque to be determined as a function of the detected rpm of the internal combustion engine. This yields the result that with the help of the rpm sensor already provided, a change in the actual torque and thus jerking or the like can be detected. No additional sensors or other additional parts are necessary.
In a first embodiment of the present invention, an expected rpm is determined as a function of the setpoint torque, and the expected rpm is compared with the detected rpm of the internal combustion engine. Thus, an rpm prediction is made. The required rpm for no irregular running is calculated. Then a determination of whether or not jerking has occurred during the shifting operation is performed on the basis of a comparison of this expected rpm with the actual rpm of the internal combustion engine.
It is advantageous if at least one of the performance quantities of the internal combustion engine is influenced when the detected rpm differs from the expected rpm by more than a preselectable rpm difference. If the expected rpm differs significantly from the rpm actually detected, it is deduced from this that there has been irregular running during the shifting operation. This then results in the actual torque of the internal combustion engine being influenced by one of the performance quantities in the sense of a reduction in the change in rpm.
In addition, it is advantageous if no influence is implemented when several successive rpm differences have an approximately steady characteristic. If there is such an approximately steady characteristic, this means that the load applied to the internal combustion engine has changed. For example, because of an inclination or the like, i.e., a change in driving resistance, the torque has changed approximately steadily, i.e., it has increased, in this case. Thus, there is no jerking and no irregular running, so no countermeasures need be taken.
In a second embodiment of the present invention, at least two rpm gradients are determined from the detected rpm of the internal combustion engine, and two of the rpm gradients are compared. Thus, the change in the actual rpm of the internal combustion engine is monitored. This is accomplished easily by calculating the rpm gradients. No additional parts or the like are required.
It is advantageous if at least one of the performance quantities of the internal combustion engine is influenced when the two rpm gradients have a non-steady characteristic. The non-steady characteristic of the rpm gradients is thus interpreted as irregular running or jerking during the shifting operation. Load changes or the like result in an approximately steady characteristic of the rpm gradients, so no jerking is deduced in this case. Only when irregular running is detected are countermeasures taken to reduce the jerking during the shifting operation.
In another embodiment, the influence on one of the performance quantities is implemented adaptively. Thus, there is a permanent correction in the shifting operation. In this way it is possible to compensate for changes in the internal combustion engine over its lifetime, in particular wear phenomena and the like. It is also possible to compensate for deviations between different internal combustion engines of the same type in start up.
In another advantageous refinement of the present invention, the influence on one of the performance quantities is not implemented until the next shifting operation. This yields the result that the calculations according to the present invention can be performed between two shifting operations, so that sufficient time is available.
It is advantageous if the injected fuel mass is influenced in the sense of an increase in particular in the first operating mode. It is also advantageous if the firing angle or the firing time is influenced in the sense of a late adjustment in particular in the second operating mode. Through these measures, it is possible when irregular running is detected during the shifting operation to influence the actual torque of the internal combustion engine and thus reduce the irregular running. In particular, the two operating modes are approximated to one another at the shifting time through these measures.
The implementation of the method according to the present invention in the form of a control element which is provided for a control unit of an internal combustion engine in a motor vehicle in particular maybe important. A program capable of running on a computer, in particular on a microprocessor, and suitable for executing the method according to the present invention is stored on the control element. Thus, in this case, the present invention is implemented by a program stored on the control element, so that this control element together with the program represents the present invention in the same way as the method for whose execution the program is suitable. In particular an electronic storage medium, e.g., a read-only memory, may be used as the control element.